ANALYZING HEAVY MINERAL SANDS FROM OFFSHORE OF THE VIRGINIA COAST USING SEM AND RAMAN SPECTROSCOPY

This research is being conducted to determine if we can develop a and cost effective way of identifying high-density (heavy) minerals that contain critical commodities such as Ti, Zr, and/or REEs within quartz-rich sand resources. Sandbridge Shoal (SS) on the Federal Outer Continental Shelf is a proven sand source for beach re-nourishment needs, and heavy mineral sands constitute an average of 0.85 percent by weight (%) of bulk material. Vibracore drilling at SS was performed by Schnabel Engineering, and cores were sampled by Virginia Energy for heavy mineral analyses. Due to the low concentration of high-density minerals in the quartz-rich samples, sediment was initially run through a Humphreys three-turn gravitational spiral to separate lighter density minerals from the high-density minerals of economic interest. This physical separation method is relatively simple and quick, although lighter-density minerals (i.e. quartz and feldspar) are still present in this first-pass heavy mineral fraction.

In this study we assess the accuracy of mineral identification using spectral and image analysis tools including a Renishaw inVia Raman microscope and a Phenom desktop scanning electron microscope (SEM) on the initial heavy mineral sand fraction. We measured five SS samples. Approximately 200 sand grains of each sample were randomly selected and mounted onto SEM mount stubs with carbon adhesive. A Leica M125 microscope was used to image the grain mounts using stacking software. The grains were then analyzed on the Renishaw inVia Raman microscope using the 532nm laser at 10% power and circular polarization. Our current results show that the initial concentrates primarily consist of quartz, along with ilmenite, kyanite, amphibole, feldspar, garnet, staurolite, epidote, and anatase. Using the Raman microscope on unpolished sand grains has proven to be an effective method of identifying minerals. Additional compositional analysis and imaging using SEM will complement the Raman technique and allow us to identify specific mineral groups. Finally, we compare our results to the data reported in Nelson et al. (2024), where the heavy mineral sand fraction was subjected to further separation with heavy liquids and laboratory-intensive electron microbeam, XRD, and LA-ICP-MS analyses performed by SGS Canada.